AFFECT/AFFECTION: Neither word denotes a personal feeling (_sentimental_ in Deleuze and Guattari). L’affect (Spinoza’s affectus) is an ability to affect and be affected. It is a perpersonal intensity corresponding to the passage from one experiential state of the body to another and implying an augmentation or diminution in that body’s capacity to act. L’affection (Spinoza’s affectio) is each such state considered as an encounter between the affected body and a second, affecting, body (with body taken in its broadest possible sense to include “mental” or ideal bodies).
—Massumi’s Definition of Affect from A Thousand Plateaus:xvi “Notes on Translation and Acknowledgments”